your system has run out of application memory

This morning just browsing the web I has a system generated invitation to 'force quit applications', the reason given is as set out in this query heading. The applications open and shown in the warning amounted to less than 1Gb. I'm using a new 2021 Macbook Pro 14" with 16gb of memory. I've recently upgraded from a 2014 MB and have never encountered this issue before.

Further I thought it would be relevant to look at the CPU system monitor but it won't open. Could these events be related?? Your observations would be appreciated